High electric fields are desirable in various electronic applications, such as flash memory, liquid crystal display (LCD) drivers, and the like. Conventionally, direct current-(DC) DC conversion methods that have been utilized to obtain high electric fields include the switched capacitor DC-DC converter, which has been shown to demonstrate properties suitable for on-chip implementation. Additionally, some existing switched capacitor charge pumps with high voltage gain are constructed via cascading voltage doublers. However, these existing cascading switched capacitor charge pump designs suffer from reverse current, body effect issues, and other factors negatively impacting performance.
Various techniques have been implemented in conventional charge pump circuits to mitigate these shortcomings. For example, a cross-coupled switched capacitor voltage doubler can be utilized to increase efficiency and voltage gain. Further, the voltage doubler can be cascaded without the output stage to realize a simplified 4× voltage converter. However, in these conventional charge pump designs, the threshold voltages of the switching transistors have to be precisely trimmed in order to prevent the reverse current problem. Accordingly, such designs require the use of expensive complementary metal-oxide-semiconductor (CMOS) processes to fabricate power transistors with two different threshold voltages, which can then be applied to implement the 4× voltage converter. While a small number of such CMOS processes exist, difficulty still persists in trimming the CMOS process for multiple threshold voltages for higher conversion ratios. In particular, it can be appreciated that the higher the conversion ratio desired, the larger the threshold voltages of the power transistors are required to be in the conventional charge pump designs described above. Accordingly, if the required threshold voltages become too large, the charge pump becomes difficult to manufacture. In addition, large threshold voltage requirements can potentially result in latch-up problems, which in turn render realization of a high voltage conversion ratio using conventional charge pump circuits substantially impossible.
In view of at least the above-described shortcomings of traditional charge pump circuits, it would be desirable to implement a charge pump circuit design that allows for high area efficiency and voltage conversion ratios.